The invention generally relates to the field of surface and shape adjustment by differential strain inducement. In particular, the invention relates to the field of compressive strain inducement into a solid structure by disrupting its structural homogeneity at selected regions.
Precision shape adjustment is a fabrication procedure with a particular need for ongoing improvement because of its use in the processing of numerous small, high-precision objects. Solid structures with a need for precision shape adjustment are for instance the sliders in hard disk drives. Sliders are manufactured to narrow dimensional tolerances, in particular at their air-bearing surface.
The air-bearing surface is designed to keep the magnetic recording head at a predetermined flying height above the rotating disk during its read and write operation. The flying height influences the achievable data storage density on the rotating disk. In order to increase storage density, the air-bearing surface must be designed to allow smaller and smaller flying heights.
The continuous miniaturization of sliders makes it increasingly more difficult to control their ever-tighter shape tolerances. Slider shape deficiencies that result from conventional manufacturing techniques become more critical for the operational performance of the slider on a disk, during contact start stop (CSS) and/or during slider load/unload operations.
Commonly, a lapping process is used that induces surface stress on selected regions or faces of the magnetic recording sliders and performs microscopic dimensional shape adjustment. The lapping process is typically carried out at the slider row level. Hence, it provides a very limited possibility to adjust individual magnetic recording heads. Further, the lapping process becomes more difficult to apply as the desired tolerances of the produced sliders become smaller.
The fabrication methods, used to create and smooth the microscopic air-bearing surface, typically generate flat, sharp edged features and contours. As an unfavorable result, air-bearing edges and corners, which occasionally come into contact with the disk, become more likely to penetrate lubrication and wear layers on the disk and scratch the magnetic layers of the hard disk. To address this problem, fabrication techniques are introduced at a late stage of the manufacturing process to induce a convex curvature to the air-bearing surface. This curvature prevents on one hand a real surface contact and stiction between the slider and the disk surface. On the other hand, the induced curvature reduces the risk of cutting or abrading the disc surface with the air-bearing surface during dynamic contact.
One fabrication technique used to induce surface curvature is known as scribing. It is described in the U.S. Pat. No. 5,704,112. The patent describes a method for mechanically forming grooves in the material on areas of the air-bearing surface. The grooves are preferably created by a diamond tip that is moved with a small load along a surface of the work piece. The description is indefinite as to how far the removal of material will enable bending of the slider by changing the stress induced on that side of the slider during its prior polishing. The use of a diamond tool with an edge angle of 120 degrees and a load of 100/150 gr is disclosed in FIG. 9 and 10. It is known to those skilled in the art that the use of such a tool in combination with materials used for the manufacturing of sliders causes at least some plastic deformation together with the removal of material. The inducement of plastic deformation is the source of compressive strain in the area surrounding the grooves. To the contrary, column 4, line 47 and following describe in an embodiment alternative creation of the grooves as shown in FIG. 3. The use of many very different material removal techniques is listed without identifying their influence on creating compressive strain.
Mechanical scribing by the use of a diamond tool requires very high precision; it is time consuming and expensive for mass production. The application of adequate gram loads on the microscopic work pieces is also problematic, because it requires additional mechanical support for the work piece. Grooved surfaces have to be accessible for the diamond tool, which puts a limitation on the design of the air-bearing surface.
Another shortcoming of mechanical scribing is the unavoidable creation of microscopic debris. Microscopic debris makes additional cleaning operations necessary and further reduces the efficiency of this fabrication technique.
A method to thermally induce tensile stress for curvature adjustment of air-bearing surfaces is described in the U.S. Pat. No. 5,982,583. The patented method uses a laser beam to melt surface areas of the back face of the magnetic recording head. During the subsequent cooling process the melted material shrinks and induces a tensile strain energy on the back face, which bends concave. As a result, the whole structure of the magnetic recording head including the opposing air-bearing surface is deformed. This is a relatively expensive process, which requires individual slider measurement and repeated laser illumination. This process also produces debris, which must be cleaned from the sliders.
Therefore, there exists a need for a clean and efficient fabrication method that enables the formation of a curvature on a predetermined area of a solid structure like, for instance, an individual slider of a hard disk drive. The present invention addresses this need.
It is an object of the present invention to provide a clean, efficient and non-destructive fabrication technique to controllably adjust the curvature of a predetermined area of a solid structure.
It is another object of the present invention to provide a fabrication technique for curvature adjustment of solid structures that is not limited by geometric and/or dimensional conditions of the work piece.
It is a further object of the present invention to provide a fabrication technique for curvature adjustment of solid structures that can be applied without causing a significant temperature rise of the work piece.
Ion implantation is typically used to implant precisely controlled amounts of material at a particle destination within semiconductor materials. The reason for that is mainly to locally change electronic properties of the semiconductor material. Commercial tools and equipment are available to perform the particle implantation. The basic knowledge of particle irradiation within a solid has been developed and implemented in commercially available engineering software.
During particle implantation the kinetic energy applied to each of the particles dissipates along their deceleration path within the structure of the material. A portion of the particle energy is dissipated by causing displacements of atoms from their original positions in the solid, leaving vacancies in the solid structure. Atoms, which are directly hit by the moving particles along the deceleration path, may recoil out of their lattice positions if sufficient energy is transferred by the impact. The recoiling atoms themselves may have sufficient energy to cause other atoms to be displaced from their sites. This continues until all kinetic energy of the recoiling atoms is exhausted.
The atomic displacement takes place in regions called cascades. The cascade center, where the atomic displacement is initiated, is typically rich with vacancies since atoms were removed. This region is often surrounded by an interstitial-rich region, produced as the rapidly diffusing interstitials leave the cascade center. Vacancies themselves can diffuse too, but typically at a much lower rate. They are also frequently refilled by an atom ejected from a neighboring site.
In a crystalline lattice, a result of particle irradiation may be a disordered crystalline lattice within the cascade region, and accompanying compressive strain energy within the cascade volume. An increase in compressive strain energy is a well-known consequence of particle implantation in crystalline materials.
It is known to those skilled in the art that in some materials, such as silicate glasses, polymers and/or amorphous alloys, particle irradiation may cause compaction resulting in tensile strain.
In the present invention, the introduction of a controlled, local strain energy is intentionally cultivated to create a modified strain region embedded in a strain reactive structure. The modified strain region is embedded at a location of the strain reactive structure and features a size, shape and a strain energy that relate to the physical properties of the strain reactive structure. As a result, a predetermined deformation of the strain reactive structure is accomplished. The relevant physical properties of the strain reactive structure include, for instance, shape, size, modulus of elasticity, Poisson""s ratio and yield stress.
Conventionally, the particle beam energy is chosen so that the principal strain occurs in a layer much closer to the surface of the material than to its reverse side, typically at a depth of a few microns. Hence, modified strain regions are created at a quasi surface location, where the altered strain can be utilized most efficiently to perform a predetermined deformation of the strain reactive structure. As a result, the processing particle energies remain at a manageable level. By limiting the mean particle current density to which the work piece is exposed, the thermal rise in the work piece can be kept low so that it does not impose any limitation in the industrial application of the method.
Even though particle implantation equipment is used in the inventive technique, the equipment is used to efficiently distort the solid structure by radiation damage, rather than to utilize it to induce chemical or electronic changes caused by the particles. Therefore, the invention is described as particle irradiation rather than particle implantation. Particle irradiation can be easily tailored to the specific needs of the work piece and/or the required dimensional precision adjustment. Non-contacting masks and/or lithographic masks may be used to restrict the particle beam to predetermined locations. A focused particle beam may be used to create the modified strain regions without any mask. Particle irradiation does not require specific surface geometries and/or extended accessibility such as are necessary for mechanical scribing as described in the background section.
Ion implantation is a clean technique with little associated debris and/or condensed vapors. This fact gains significance when the work piece becomes too small and sophisticated for reliable cleaning with a feasible effort.
During conventional particle implantation for semiconductor doping, particles of a required material must generally be placed in a solid structure with a minimal crystalline distortion, whereas particle irradiation utilizes particles with an optimized distortion characteristic to achieve a desired macroscopic distortion. Hence, for particle irradiation, the particles are mainly selected for their distortion properties on the work piece material following their impact. Appropriate particles are, for instance, Argon, Helium, Hydrogen, Boron, Nitrogen, Carbon, Oxygen and Neon in combination with Titanium carbide/Aluminum oxide material for the strain reactive structure. It is clear to one skilled in the art that any other particle types may be used to create strain regions in a broad range of other strain reactive materials.
The strain-inducing particle irradiation is primarily characterized by the particle element species, particle dose, particle energy and particle impact angle. The result is a specific strain energy and consequently a deformation of the workpiece.
In a simplified case, when the modified strain region uniformly covers an exposed surface, the achieved deformation curvature in a profile section is convex and is proportional to the thickness of the modified strain region and to the inverse of the second power of the material thickness.
The modified strain region may be embedded within a strain reactive structure of the same and/or different material. In such cases, the achieved deformation depends on the combination of the geometry and elastic properties of the modified strain region, the strain reactive structure and the embedding relation between them.
The present invention is preferably utilized to add and/or adjust a curvature of the air-bearing surface of magnetic recording heads. The particle irradiation is performed in a late stage of the manufacturing process after the heads are finished, and after most or all of the slider shaping is complete.
Metal and/or photoresist masks are used to protect sensitive areas against the irradiation. Masks may be used further to create the modified strain regions with predetermined a real shapes. The selection of specific a real shapes makes it possible to apply the curvature in a predetermined direction. The irradiation process itself may be applied sequentially on a number of cyclically exposed work pieces such that the particle beam power can be brought to a maximum without exceeding a critical thermal rise in each work piece. Thus, during the irradiation process, the beam power becomes averaged over many work pieces.
The irradiation beam may be repeatedly scanned onto the work pieces to accumulate the desired strain. Alternatively, the work pieces may be repeatedly moved into the irradiation beam for the same desired effect.
The particle irradiation may be used to perform a dimensional precision adjustment of many material structures, as for instance, for the adjustment of optical elements in opto-electronic devices and/or the tuning of cantilevers.